Cold cathode gas tube trigger pulse circuit



Patented Apr. 25, 1950 7 COLDVCATHODE GAS TUBE TRIGGER PULSE Clifford J. Craft, 3rd, Flushing, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York I Application April 29, 1949, Serial No. 90,501

9 Claims. (01315-271) This invention relates generally to trigger pulse circuits and more. specifically to trigger pulse circuits employing cold cathode gas tubes.

"One of the objects of this invention is to produce a low current trigger pulse output voltage which approaches the peak value of the alternating input voltage applied to a pulse generating circuit.

. Another object of this invention is to obtain a high impedance trigger pulse voltage source.

A third object is improvement of cold cathode 1 gas tube trigger pulse circuits generally;

The trigger pulse circuit employed in thislnvention utilizes a gas tube having a probe therein. The gas tube employed conducts current in either direction. Because of this characteristic of I the tube, the electrodes that would normally be designated as the main cathode and the main anode of the tube are herein defined as cathanodes. One of the cathanodes, however, has a much larger surface area than the other which results in a larger current flowing in the tube when the larger of the two cathanodes acts as the cathode as compared to that which flows when the smaller of the two cathanodes is utilized as a'cathode. A .current limiting resistance is connected to the large area cathanode, and analtcrn-ating voltage is applied across this resistance and the gaseous space path between the two cathanodes. The I aforementioned probe is connected to the potential, source side of the current limiting resistance through a load resistance." The output pulse voltage which is developed-across the load resistance tends to follow the potential withrespect to ground of the particular cathanode which acts as an anode for a giveninput-hali cycle from said alternating voltage source.

A feature of the invention is theuse of the probe as an active element in the trigger pulse circuit, said probe having a large resistance connected thereto to produce a high impedance trigger pulse voltage source.

This and. other features of the invention: will be more fully understood from the following detailed description of the drawings and mode of' 2 cold cathode gas tubes having a starter anode therein.

. Fig. 6 illustrates graphically the distribution of the instantaneous applied line voltages over the circuit components of the circuit shown in Fig. 5.

In Fig. 1 there is shown a circuit for the generation of 140-volt output trigger pulses every other half cycle of the 150-volt, Gil-cycle source 6. Element 1 is a cold cathode 3-element gas tube, one of the three elements being probe 4. The other two elements comprise a cathanode and cathanode 3. The term cathanode is used herein to define an element of a gas tube which may be used either as a cathode or an anode, depending upon the polarity of the voltage applied to the tube terminals. In the exemplary embodiment of the invention described in this specification, cathanode 5 has a much smaller surface area than does cathanode 3, with the result that a given voltage applied across the gas tube will produce more current in one direction than will be produced when the polarity of said voltage is reversed. Resistance 2 in the probe circuit has a value of approximately 4 megohms. Resistance I has a value of approximately 10,000 ohms.

Figs. 2 and 3 graphically show the current vari- 'ations within the tube of Fig. 1 as the potential between the two cathanodes of the tube is varied in amplitude and polarity. It will be noted that voltage source 6 is impressed across the tube and -,Fig. 5, shows, a trigger pulse circuit employing resistance I. This figure will be more fully described below concurrently with the discussion of the operation of the circuit shown in Fig. 1.

In Fig. 5 resistances 2|, 26 and 28 have values approximately of 4 megohms, 5 megohms and 5,000 ohms, respectively. Capacitance 25 is 1 microfarad and alternating voltage source 29 has a peak value of volts.

Fig. 6 was taken from an oscilloscope screen and shows the distribution of the applied voltage over various portions of the circuit. V29 is the line voltage. V24 represents the probe voltage and V21 illustrates the cathode voltage. The operation of the circuit shown in' Fig. 1 depends on the following principles and design. -Tube 1 is capable of conducting current in'either direction. For conduction in one direction volts. 7

Resistance I has been chosen so that approximately 5 milliamperes willbe conductedthrough tube 1 when cathanode s is utilized as thecathode and alternating voltage source 6 has a peak value of 150 volts. The sustaining voltage of tube 1 will be approximately 100 volts. Since the probe 4 seeks a potential which is about 10' volts below the anode 5 voltage, the probe potenrtial will reach a peak value in the neighborhood of 140 volts. The first half cycle shown in Fig.

4Jillustrates the conditions existing in the circuit during this time. .-;designated as VAC is the sustaining voltage of "171 1851311116. Thevoltage VB shows the potential of the probe during this half cycle. It is to be noted -ithat inasmuch as anode 5 is of the same poten- The voltage across AC tialxas line voltage i5 and probe 4 is only 10 volts be'low the potential of anode 5, that therefore the 1 potential of probe 6 is about 140 volts at the peak value of this halfv cycle of the applied voltage 6.

When voltage source 5 reverses, element 3; acts tube 1 at the first instant of ionization are shown in Fig; 2 by the intersection of the 10,000-ohin i'load line with the current-Voltage curve at point 0 When the voltage". from source 3 attains a value of 1201vo1ts, tube 5 breaks down and immediately assumes. the values shown by the intersection point :9. subsequently,.source t attains a" peak :vo'ltage of 150 volts,at which time a peak current v toii2 milliamperes passes through the tube as is also indicated in Fig. 2. As in the firsthalfcof the cycle the probe it tends to assume a potential value approximately 1e volts-below thespo'tential of the element: which. now is -actin uas: theaanode which now elementt. Fig. illustrates: ithe distribution: of the appliedvoltage during this half oi: thezoycle; Element 5 isizat the voltage applied: by source-5t: and anode--13 is ati.'the same said voltagerminus. the sustaining voltagerwhioh increases to a :value: or approximately- 130 volts when z miliiamperes flow through "tube 1, thus placing. ano'deei3;-at approximately 29 .volts minus atithezpeakvalue of this cycieofthe applied voltage-6. Sinceprobe-tassumes a valuelofzpotential of about-1'0 VORS 'bBIOWI'ChaU of anode .3:' the potential of. probe isrnownabfout 30 volts minus.

From "the: above description". of the circuit shown in. Fig. .1' it is apparentv that a pulserof about 140 voltsisrproduced on probe duringLthe :halftoycle oiithe applied voltage from'sou'rce'fi in which elementsEr: is utilized aszan'ianode a-n'd that ,a second pulse. having apeak value of 30volts istproduced on probe 4 during that part-i fthe cycle ,oithe- -applied voltage fromwsourceifi w-hen selementtipis acting as the-anode. The :large =dif- For example, at 2 milliam peres the sustaining voltageis approximately. 130

iernce in the values of these two pulses allows discrimination between the two pulses and as a jc' 'onsequence the use of the larger of the two pulses trigger pulse.

- a probe is added to the conventional triode having a starter anode, a unidirectional pulse Jvdlt'age can'sbegobtained. "The tube is placed in a-e-i'rcuit in sucha manner that'it conducts current only in one direction, during every other half cycle, when an alternating voltage supply sourceisapplied. .In Fig. 5 there is shown a cirduit'for a possibl'application of this embodiment 'o f .the invention. The gas tube used in this circuit must be-chosen with certain requirements in n'iiiid. T he starter anode to probe and the main anode to probe breakdown voltages must be veryhigh sothatbreakdown between the starter anode and the probe or the main anode and the presences not occur thereby ionizing the tube at an undesired time. Furthermore, the tube must liaveth'e' characteristic oi-itran'sferring conduction from-starter anode to main-anode when said anodes. are positive with respect to'the cathode, but must not-transferoonduction from the starter :anode toythe main anode when the cathode is positive withsrelationlto' said anodes. Thus, the tube must conduct current in one direction from the starter anode and the main anode to the cathode but must only be .capable'of conducting current in the: reverse direction from the cathode :toathe starter anode.

In Fig.-i.5.-the probe. 24iis connectedto the cathode 2T through..-a.resistance and capacitance arranged .inparallel.- As starter ano'd'e22 becomes positive with respect to xoathode' 21, breakdown occnrs inthe'sstarter anodei2'2 main cathode 27 -ga pandsubsequently-transfers to the main anode -23 main cathodeifl gap; When this occurs, the potential .ofiprobez241zrises to aval'u'e' of about .mfilowvoltsrl'essthan the potential of main anode zs whichis at line' voltage. During this time -comler1serf25 is charged to the probe potential :andlwher'i the xsupply voltage 29 decreases to a pointzinsuificient to sustain ionization between Aslthemainaanod 23La rl'd tlre'rnainkanode 21, the

ttubezextingnishes butithetcharge of condenser 25 :maintainstheaprobe potential 'at a value shown .i Fig. fi-haridtdesignate dvzi. Agradual dissipaition of:thisi'icharge xtakeslplace through the very so laiige' neSistmicxN-mntili such time a's-the cycle is repeated andwmainaanode 23" onceagainbearc'qr nes a-zconducting :elementgwhereupon the po- .itential of;probdfi'rises sharply again asis shown .It is to beunderstood thatthis specification ,onl yedescrlbes exemplaryiembodiments or the invention and various ch'ang'es in' -the selection of :circuit:elementsmnd in the circuit arrangements may "be; made withoutdeparting from the spirit somrsscope' ofxthe :inve'ntion.

. *Whatis 'claiined is'c .1. A trigger voltage pulse generating circuit acompr'is'iiig la cold cathode' -gas'tube, a plurality of e exits with'iiisaid'gas 'tube including a i357 piob'ei said gas tube 'beiiig capable of conducting current bilaterally between the elements therein .wh'e'ri an alternating voltage is applied across said gas- -tulie,said-probe being connected to one -other oisaid'pliirality of elements through an mdmpedance ne'twork; and an alternating voltage sourei applied across said gas tube and said impedance network.

izt-mitri-gger voltage pulse generating circuit comprising a cold cathode gas tube, a pluralityof ."issclements withinsaid iigas itube including a probe and a cathanode, said gas tube being capable of conducting current bilaterally between a plurality of said elements included therein when an alternating voltage is applied across said gas tube, said probe being connected to said cathanode through an impedance network, and an alternating voltage source applied across said gas tube and said impedance network.

3. In a trigger pulse circuit, a gas tube comprising a first cathanode, a second cathanode, and a probe, said gas tube being capable of conducting current from said first cathanode to said second cathanode, and also being capable of conducting current from said second cathanode to said first cathanode, said current in one direction being larger than said current in the other direction for a given voltage applied across the cathanodes, a first resistance connected to said first cathanode, an alternating potential source applied across said first resistance and said second cathanode, and a second resistance connecting said probe to said first resistance.

4. In a trigger pulse circuit, a cold cathode gas tube comprising a first cathanode, a second cathanode, and a probe, said first cathanode having a larger surface area than said second cathanode, said gas tube being capable of conducting current from said first cathanode to said second cathanode and from said second cathanode to said first cathanode, said current in one direction being larger than the current in said other direction for a given value of potential applied across said cathanodes, a first resistance connected to said first cathanode, an alternating voltage source applied across said first resistance and-said second cathanode, and a second resistance connecting said probe to said first resistance.

5. A trigger voltage pulse generating circuit comprising a cold cathode gas tube, said gas tube comprising first and second cathanodes and a probe, a first resistance connected to said first cathanode, an alternating voltage source applied across said gas tube and said first resistance, and a second resistance connecting said probe to a junction between said first resistance and said alternating voltage source.

6. A trigger voltage pulse generating circuit comprising a cold cathode gas tube, said cold cathode gas tube comprising a first cathanode, a second cathanode, and a probe, said first cathanode having a larger surface area than said second cathanode, and said gas tube being capable of conducting current bilaterally between said cathanodes, said current in one direction being larger than the current in the other direction when an alternating voltage is applied across said gas tube, a first resistance connected to said first cathanode, an alternating voltage source applied across said first resistance and said second cathanode, and a second resistance connecting said probe to a junction between said first resistance and said alternating voltage source.

'7. A trigger voltage pulse generating circuit comprising a cold cathode gas tube having a plurality of elements including a probe, said gas tube being capable of conducting current bilaterally between the elements therein when an alternating voltage is applied across said gas tube, a first resistance connected to one of said elements, an alternating voltage source applied across said as tube and said first resistance, and a second resistance connecting said probe to a junction between said first resistance and said alternating voltage source.

8. An electrical circuit comprising a cold cathode gas tube comprising a first cathanode, a second cathanode, and a probe, said gas tube being capable of conducting current from said first cathanode to said second cathanode, and also being capable of conducting current from second cathanode to said first cathanode, said current in one direction being larger than said current in the other direction when an alternating voltage source is applied across the cathanodes, a first resistance connected to said first cathanode, an alternating potential source applied across said first resistance and said gas tube, and a second resistance connecting said probe to said first resistance.

9. A trigger pulse voltage generating circuit comprising a cold cathode gas tube, said cold cathode gas tube comprising a starter anode, a main anode, a main cathode, and a probe, an impedance network including a first resistance and a capacitance in parallel connecting said probe to said main cathode, a second resistance connected to said main cathode, and an alternating voltage source applied across said main anode and said second resistance.

CLIFFORD J. CRAFT, 3RD.

No references cited. 

